The ultraviolet (UV) light was discovered in 1801. In 1877, British scientists used the UV light to irradiate and kill Bacillus subtilis and Bacillus, which confirmed the ultraviolet disinfection. Deep UV lights with the wavelength ranged from 200 nm to 280 nm could directly damage the links of the deoxyribonucleic acid (DNA) and the Ribonucleic acid (RNA) in the bacteria and the viruses, and the sterilization effect is unrelated to the bacterial species. The sterilization efficiency may be ranged from 99% to 99.9%. Among these deep UV lights, the UV light of the wavelength ranged from 250 nm to 270 nm has the strongest sterilization effect.
The sterilization effect of the UV light is related to the irradiance, the irradiation time and the conditions of the object to be sterilized. Although enhancing the irradiance and the irradiation time of the UV light could increase the sterilization effect, the non-uniform distribution of the irradiance and the long irradiation time would not like to be seen by the designer or the user. Therefore, how to enhance the sterilization efficiency and the sterilization effectiveness of the UV light under an appropriate irradiance and an irradiation time becomes one of the important issues to be solved.